1. Technical Field
The present invention relates to a circuit device and an electronic apparatus or the like.
2. Related Art
A technique of controlling the number of revolutions of a motor by controlling a chopping current is known as a technique for a motor driver that drives a DC motor. In this technique, a current flowing to an H-bridge circuit is converted to a voltage by a sense resistor, and the resultant voltage is compared with a reference voltage, to detect a chopping current. The detection result is fed back to a control circuit, to perform PWM control of a drive signal for the bridge circuit, thereby rotating a motor at a fixed rate. As such techniques for a motor driver, the techniques disclosed in JP-A-2003-189683 and JP-A-2008-042975 are known.
The H-bridge circuit of the motor driver has first to fourth transistors (switching elements) for driving, where the first and fourth transistors, and the second and third transistors, are connected electrically diagonally with respect to the motor. During the charge period, the first and fourth transistors are on, whereby the positive-side (+) terminal of the motor is set to a high-potential voltage and the negative-side (−) terminal is set to a low-potential voltage. During the decay period, the second and third transistors are on, whereby the positive-side terminal of the motor is set to a low-potential voltage and the negative-side terminal is set to a high-potential voltage. A drive current is thus allowed to flow to the DC motor, to perform drive control of the motor.
Such a motor driver is provided with a pre-driver circuit that outputs a drive signal to each of the transistors of the H-bridge circuit. In this case, in order to apply a proper voltage between the gate and source of each transistor of the H-bridge circuit, it is desirable to provide a bias circuit that supplies a bias voltage as a power supply voltage that sets the low or high level of the drive signal.
However, if a failure occurs in the bias supply circuit, etc., the gate voltage of a transistor of the H-bridge circuit may become abnormal, causing gate breakdown, etc., and this may result in flow of an overcurrent. If such an overcurrent flows, there is the possibility that breakdown, etc. of the motor may occur.